No description available.

No description available.

Une diminution de l’étendue du couvert de glace et de neige au printemps a été observée en Arctique. Il est attendu que ceci affectera la phénologie des floraisons printanières, de même que la succession des groupes et espèces parmi les producteurs primaires. Les principaux objectifs étaient (i) de caractériser les communautés d’algues de glace et de phytoplancton et (ii) d’identifier les principaux forçages environnementaux associés à la succession des principaux groupes taxonomiques d’algues unicellulaires pendant une floraison printanière en baie de Baffin en 2015 et en 2016. Avec des mesures de variables environnementales à haute résolution temporelle et utilisant un cytomètre en flux imageur submersible (Imaging FlowCytobot) pour l’identification et le décompte des algues (<150 μm), nous avons évalué le rôle de la lumière et de la disponibilité en nutriments dans le contrôle des floraisons printanières d’algues unicellulaires. Les diatomées pennées représentaient principalement les communautés sympagiques. Les communautés phytoplanctoniques étaient initialement semblables à celles observées dans la glace, suggérant un possible ensemencement des floraisons phytoplanctoniques par les algues de glace. Une augmentation de l’intensité lumineuse, principalement causée par la fonte de la neige et l’apparition de cuvettes d’eau de fonte, semble avoir favorisé les diatomées centriques, ces dernières dominant les communautés pélagiques pendant les floraisons phytoplanctoniques des deux années. La disponibilité en lumière semble être le forçage principal limitant le déclenchement des floraisons sympagiques et pélagiques, avec une valeur journalière minimale de 0.1 mol photons m-2 d-1. Une limitation en nutriments dans la glace n’a pas clairement été observée, alors que les nitrates semblent avoir joué un rôle prépondérant dans le déclin de la floraison dans la colonne d’eau. Nos résultats suggèrent qu’il y a un fort potentiel pour des floraisons printanières sous la glace, qui sont actuellement principalement limitées par la lumière tôt dans la saison. / With ongoing climate change in the Arctic, a decrease in the extent of sea ice and in the spring snow cover thickness has been observed. A modification of the ice and snow dynamics is predicted to impact the onset, the duration and the decline of microalgae spring blooms, as well as the succession among groups and species of primary producers. The main goals of the present study were (i) to characterize the ice-associated algae and phytoplankton communities and (ii) to identify the main drivers associated with the microalgal main taxonomic groups succession during an under-ice bloom in Baffin Bay in 2015 and 2016. With high-resolution time series of environmental parameters and using an Imaging FlowCytobot for the identification and enumeration of algal cells (<150 μm) within the sea ice bottom and in the underlying water column, we address the role of light and nutrients availability in controlling spring bloom phenology. Pennate diatoms dominated the sympagic community, with different genera dominating for each year. The phytoplankton community was initially alike that found in sea ice, suggesting a possible seeding of the pelagic bloom by the ice algal community. Light availability seemed to be the main factor controlling the onset of both sympagic and pelagic blooms, with a threshold value of 0.1 mol photons m-2 d-1. Through spring, snow and sea ice melting in association with melt pond onset caused the decline of the sympagic bloom, while the increase in under-ice irradiance likely favored centric diatoms, which dominated the protists assemblage during the phytoplankton blooms. Nutrients limitation in sea ice was not observed, while nitrate seemed to play a major role in the decline of the phytoplankton bloom. Our results suggest that there is a potential for early and massive under ice blooms, which are mostly light limited early in the season.

Les micro-organismes constituent 90 % de la matière vivante océanique. Parmi eux, le Crenarchaeota Candidatus Nitrosopumilus maritimus a récemment été isolé, révélant que les membres du même clade sont responsables d'une grande part de la nitrification, dans le cycle de l'azote. Ce potentiel biochimique est détecté chez les Crenarchaeota avec une approche moléculaire, avec la présence et l'expression du gène de la sous-unité A de l'ammonium monooxygénase (amoA). L'environnement échantillonné, la région des Eaux du Nord (Nord de la Baie de Baffin, entre l'île Ellesmere et le Groenland) a une productivité biologique parmi les plus élevées en Arctique. Celle-ci résulte notamment d'apports externes de nitrate, le produit final de la nitrification. Les résultats obtenus démontrent que le gène amoA était abondamment présent et exprimé dans les Eaux du Nord, que sa distribution et son expression étaient influencées par certains paramètres environnementaux et que sa diversité phylogénétique différerait entre les analyses basées sur l'ADN (présence) et l'ADNc (expression).

The 62 million year old lava flows of Baffin Island and West Greenland represent the earliest phase of magmatism in the North Atlantic Igneous Province (NAIP). These picritic lavas are characterised by high magnesium contents owing to their high proportion of olivine crystals. The parental magmas for the picrites are likely to have accumulated olivine crystals on their transit through the lithosphere and crust. Debate over the origin of accumulated crystals in the lavas results in uncertainty in the temperature and composition of the parental magmas for the early NAIP. The magnesium-rich olivine crystals (up to Fo93) in the picrites of this study are shown not to have a xenocrystic origin. The samples, therefore, support the inference of high potential temperatures for the Baffin Island-West Greenland magmas, ~200oC above ambient mantle. The picrites of Baffin Island and West Greenland display the highest terrestrial magmatic 3He/4He (up to 50 Ra, where Ra is the atmospheric value 1.39 x 10-6), values that are considerably higher than the highest 3He/4He in contemporary ocean island basalts, which reach a maximum of ~30 Ra. High 3He/4He in Baffin Island and West Greenland are associated with a wide range of incompatible trace element and lithophile radiogenic isotopic compositions, not dissimilar to the range of compositions displayed by lavas at mid-ocean ridges, and overlapping the range displayed by most northern hemisphere ocean island basalts. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks are mixed with depleted parents cannot account for the compositional trends displayed by the picrites. Major and trace element compositions were determined on melt inclusions in high- 3He/4He picrites that span a wide range of whole-rock incompatible trace element and radiogenic isotopic compositions. The melt inclusions support the findings from the whole-rock study since melt inclusion compositions reflect the composition of their associated whole-rock, with no anomalous compositions present. In addition, there is no evidence for a contribution of a proportion of depleted melts to the source of the relatively enriched whole-rock samples. Therefore, since all melt inclusions were contained within high-3He/4He samples, it is shown that high 3He/4He is a feature of both depleted and relatively enriched melt compositions. The wide range in whole-rock compositions of the Baffin Island and West Greenland picrites represents that of the sub-lithospheric mantle source region and is inconsistent with derivation of the picrites from residues of ancient mantle depletion. The apparent decoupling of helium from trace elements and radiogenic isotopes is hard to reconcile with simple mixing of a high-helium concentration, high-3He/4He reservoir with various depleted and enriched helium-poor mantle reservoirs. It is possible that primordial helium has diffused into a reservoir with a composition similar to that of the convecting upper mantle. However, this must have occurred after the development of existing mantle heterogeneity. The high-3He/4He picrites require the existence of a deep, primordial helium-rich reservoir. Whether this reservoir is present in the upper or deep mantle, or even the core, remains uncertain.

Deux carottes sédimentaires de la partie centrale de la baie de Baffin (HU2008029-14B et -16TWC; 70.46°N 64.66°W; ~2060 m) ont été échantillonnées afin de reconstituer les conditions hydroclimatiques holocènes à partir de l'analyse des assemblages de dinokystes. Des mesures 14C sur des carbonates biogéniques et des analyses de 210Pb sur le sédiment révèlent de très faibles vitesses de sédimentation, inférieures à 4,5 cm/ka. Un changement dans les assemblages de dinokystes est enregistré à 16 cm dans la carotte 16TWC, ce qui correspondrait à la fin de l'Holocène moyen, i.e. vers 4000 ans BP, si on postule des vitesses de sédimentation uniformes au cours de l'Holocène. La transition est marquée par une diminution de pourcentage du taxon polaire Impagidinium pallidum et par l'augmentation des proportions du taxon ubiquiste Operculodinium centrocarpum. Elle correspondrait à un réchauffement des eaux de surface que l'on associe à une pénétration plus importante des eaux nord-atlantiques via le courant ouest groenlandais. Les reconstitutions quantitatives des conditions de surface avec la technique des meilleurs analogues indiquent des conditions optimales, plus chaudes que l'actuel avec un couvert de glace moins étendu pendant la plus grande partie de l'Holocène supérieur. De tels résultats sont compatibles avec l'hypothèse d'une opposition des changements océanographiques dans le nord-ouest de l'Atlantique Nord par rapport à ceux du secteur nord-est. Les données suggèrent également des changements récents dans la baie de Baffin qui semble être extrêmement sensible vis-à-vis des variations hydroclimatiques liées aux courants de la Terre de Baffin et ouest groenlandais. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Holocène, baie de Baffin, dinokystes, paléocéanographie

The hunting economy of Cumberland Sound is analyzed according to the spring, break-up and open water seasons. Physical, biological and cultural factors interact in different manners and degrees to produce seasonal variations in the miles travelled per hunt, the duration of the hunt, the catch per man per day, the percentage loss of seals due to sinking, the miles travelled per seal landed, and the number of shots fired per seal killed. If the hunt is mechanized during all three seasons, then in terms of number of seals landed per hunter per day and net profit per landed seal, hunting is most efficient during the break-up season.

No description available.

A simple linear reduced-gravity ocean model is developed to simulate the North Water polynya located in northern Baffin Bay. The model is an extension of Pease (1987) latent-heat model for a coastal polynya. Both northerly surface wind forcing and coastal upwelling processes are taken into account in modelling the steady state and time-dependent water velocities, upper layer depth, and polynya width measured southward from its northern boundary. Also, both uniform and variable wind forcing are considered. In most of this thesis a semi-infinite domain model is used in which upwelling occurs along the eastern boundary (the Greenland coast). It is found that the steady state polynya width is a strong function of the air temperature, but a weak function of the wind speed. The model results show that in the upwelling region near the Greenland coast, the polynya width is larger than further offshore (distance $>$ 2 Rossby radii), where it is a constant (the limiting Pease width). For a variable wind forcing, the southern ice edge of the North Water has a form that is similar to that of the wind forcing. In a channel, upwelling occurs in the eastern part and downwelling in the western part. Thus the polynya is much wider near Greenland and narrower near the Canadian Islands.

Free and open source geographic information systems (GIS) and spatial data are readily available to use in spatial-archaeological problem solving. Greater accessibility allows more frequent experimentation with archaeological GIS methodologies. The least cost path (LCP) analysis has been a frequently used method in archaeological GIS. Showing potential mobility patterns between archaeological sites or between sites and resources has been the LCP’s primary objective. The LCP’s major flaw is that is must be calculated between two designated points. A recent terrain analysis of southern Baffin Island has been unable to overcome this flaw, because of the size of the study area and the inability to assume any two points are directly related. Thus, a new GIS method using a ‘watershed’ function has been manipulated to incorporate the cost-surface element of the LCP into a mobility model by generating pathway networks instead of narrow A to B paths. The product is a multitude of potential pathways linking archaeologically dense coastal and interior areas. Portions of these pathways correlate with historic geographic descriptions of Inuit travel routes and with areas where chert toolstone is accessible. Generated with no material cost, this analysis has produced a predictive model to help in future research.